1. Field of the Invention
The present invention relates to a hybrid-type stepping motor applicable to three phases and four phases.
2. Description of the Prior Art
As prior art hybrid-type stepping motors, most of the motors are of 2-phase type, and it is structured as shown in FIGS. 1A and 1B.
In FIGS. 1A and 1B, the reference numeral 1 designates a stator housing, 2 designates a stator core and it constitutes magnetic poles 2a to 2h.
The reference numeral 21 designates pole teeth formed in an inner periphery of each magnetic pole.
The reference numeral 3 designates stator windings, and each winding is wound about each magnetic pole as designated by numeral 3a to 3h.
These stator core 2 and the stator windings 3 constitute a stator S.
The reference numerals 4 and 4' designate end brackets, and 5 and 5' designate bearings.
The reference numeral 6 designates a rotor shaft, 7 and 8 respectively designate rotor magnetic poles, 7a and 8a respectively designate pole teeth formed in outer peripheries of the rotor magnetic poles 7 and 8, numeral 9 designates a permanent magnet, and a rotor R is constituted by these members 6 to 9.
Here, among the indexes representing the performances of a stepping motor, there is a step angle .theta..sub.s as an important index.
Normally, the step angle .theta..sub.s is determined by the number of phases P of the stator windings and the number of pole teeth formed in the rotor magnetic pole, and it is expressed by the following equation. EQU .theta..sub.s =180/PZ(degrees) (1)
Here, P is the number of phases of the stator windings, and Z is the number of pole teeth formed in one magnetic pole.
The step angle .theta..sub.s shown in equation (1) is an angle obtained in the case of one phase excitation in which the windings of one phase are sequentially energized, or two phase excitation in which the windings of two phases are sequentially energized, and it is inherent in the stepping motor.
When the step angle .theta..sub.s is made small, a stepping motor having a high resolution is obtained, and it is possible to improve the control performance. Thus, there are various working examples.
The equation (1) indicates that when the number of phases P and the number of pole teeth Z in the denominator are increased .theta..sub.s becomes small.
The step angle of a prior art 2-phase permanent magnet type stepping motor is represented by: EQU .theta..sub.s =180/2Z,
and in order to make it a minute angle, Z is required to be large, that is, to make a rotor tooth width small. However, to achieve this, there has been a limitation due to restriction in the machining technique.
On the other hand, it may be considered to increase the number of phases P to 5 (five) phases. However, in this case, there has been a problem in which the number of switches in a driving circuit is increased, and the circuit becomes complicated and expensive.